Detailing of architectural constructs has traditionally been several times more labor-intensive than completion of the basic structure. For example, the fitting of a louver or vent, window or door in an aperture in a building wall or roof has heretofore required several steps, including constructing the sash (or louver or vent), constructing the frame, adapting insulating materials and/or weather fins to the shape of the aperture, and securing all structures in the appropriate relative positions.
When apertures having curved edges--such as are designed to receive half--round windows--were finished according to the prior art, even greater finishing efforts were required than for straight-edged architectural features. Not only were half-round and other curved windows and doors difficult to design and to build in place, but the required weatherproofing materials were not easily adapted from their intrinsically straight configurations to the curved window or door surfaces. For example, the J-channel flashing well known in the building arts as a flashing on the sides and headers of masonry-veneer wood frame exterior wall openings is simply not adaptable to bending around a curved surface without concomitant rippling and distortion. The rippling and distortion tendencies not only take additional time on the part of the craftsman or builder, but ultimately do not permit the weather-tight construction for which the materials are used in the first place. In other words, carpentry finishing of any wall or roof aperture is time consuming, and in the case of curved or round apertures the best hand carpentry may still fall short of the ideal. A need therefore remains for a window unit which meets all of the aesthetic and mechanical requirements for finished apertures in walls or roofs and yet which can be installed with a minimum of time and labor.